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Tactic - of a movement made by a whole organism, or by a freely motile part such as a gamete, in response to a directional stimulus which has a direct bearing on the direction of the elicited response.
See also: Phototaxis
Tannin - a heterogeneous group of astringent phenolic substances, widely distributed in plants, and commercially used in tanning, dyeing and preparation of ink.
Taproot - a primary root growing straight down from a plant, and larger or longer than the branching fibrous roots. Often a thick storage organ as in a carrot.
Tardiflora (-us, -um) - late flowering.
Tardifolia (-us, -um) - late into leaf.
Taxon - a formally described category of individuals, distinct by some visible characteristics.
Taxonomy - the system and practice of classification.
Tectora (-um) - of roofs.
Teeth - sharp, pointed triangular structures arising on leaf margins.
Temperate - a climatic zone between boreal and tropical. Regions between the tropic of Cancer and the Artic Circle or the tropic of Capricorn and the Antarctic Circle.
Tender - of a plant plant that needs a minimum temperature of 60°F, although occasional brief periods of lower temperatures may be tolerated.
Tendril - a slender leafless side-shoot, often coiling around other objects, produced by many climbing plants as an aid to climbing and support.
Tenui - slender, thin.
Tepal - any of the modified leaves making up a perianth.
Terminal - borne at the end of a stem, branch or other structure e.g. terminal spine located at the end of a leaf.
Terrestrial - growing in or on the ground.
Tessellate - a surface patterned like a mosaic or pavement. Hence tessellata.
Testa - the outer protective seed-coat.
Testicular - in the form of two oblong bodies .
Tetra - four, as a prefix.
Tetrad - a group of four.
Thallus - a multicellular plant body, usually flat and not organized into roots, stems, leaves or vascular system.
Thermotropism - bending, growth or movement of a part under the influence of a heat source.
See also: Tropism.
Thigmotropism - or- Haptotropism - a growth response to a touch stimulus.
See also: Tropism.
Thorn - a sharp woody outgrowth from the epidermis which unlike the spines of Cactaceae contains vascular tissue and arises from the underlying tissues (phylogenetically as a modified stem). Because of this, breaking a thorn off the plant damages the surrounding tissue.
Compare with spines.
Throat - the visible portion of a flower between the limb and tube.
Thyrse - a dense cylindrical or ovoid inflorescence, a compact panicle; branched, the main axis indeterminate and the lateral branches determinate (i.e. with a terminal flower) or as a cyme.
Tissue - any part of an organism consisting of aggregated cells with a similar structure and function.
Tomentum - a layer of matted woolly threads on the surface of a plant. Often the hairs are white, giving the surface a silvery appearance. Latin="cushion stuffing"
Tomentose - of a surface covered with tomentum.
Tomentous - of a surface covered with tomentum.
Tomentosum - epiphet of a plant covered with tomentum.
Tortuous - twisted.
Tracheid - a basic primitive unit of the xylem (fluid-conducting tissue), consisting of a single elongated cell with pointed ends and a thick, pitted secondary cell wall composed of cellulose thickened with lignin. The mature tracheid is dead and empty of cytoplasm. Tracheids are found in all vascular plants and are the only conducting elements in gymnosperms and ferns.
Tracheary - of conducting tissues containing tracheids and vessels.
Trans-Pecos - of territory in Texas west of the Pecos River.
Transpiration - loss of water vapour through the plant's stomata. C4-metabolic adaptations in the Cactaceae and other succulents allow transpiration to be minimised.
Transverse - across or at right angles to the vertical.
Trap - a structure designed to catch and detain animal prey.
Tree - a plant with a single distinct trunk between the ground and first branch.
Traumotropism - bending, growth or movement of a part as a response to wounding.
See also: Tropism.
Trichome - a hair-like structure growing at one end from the plant's epidermis. Trichomes have numerous forms including branched or unbranched hairs, scales and glands.
Tridentate - forked into three points.
Trifoliate - a compound leaf with three leaflets.
Trigger hair - a specialized structure found in the traps of certain carniverous plants which causes the trap to activate in response to stimulation.
Trigonous - with a three-cornered, triangular cross section.
Tropism - Tropic - of a movement by a fixed part of a fixed plant towards or away from a stimulus such as gravity, heat or light, the direction of movement being determined by the direction from which the stimulus originates. A tropism is caused by a positive or negative growth response on the side of the organ nearest to the stimulus relative to the side furthest from the stimulus, and the whole organ then bends away or towards the stumulus respectively. See also: Chemotropism, Galvanotropism, Geotropism, Hydrotropism,Phototropism, Rheotropism, Thermotropism, Thigmotropism. Traumotropism,
Truncate - ending suddenly as if cut cleanly off.
Trunk - the main woody stem of a tree supported and directly attached at the lower end to the roots and at the upper end supporting the branches.
Tube - a narrow flower structure formed by fusion of the tepals.
Tuber - a thick, fleshy underground modified root or stem section used for storage of food or water, as in a potato.
Tubercle - small, rounded prominence or knob-like protusion from the surface. In Cactaceae a roughly pyrimidal protrusion from the stem surface, with an areole at or near its summit. Hence: adj. tuberculate.
Tuberculate - having tubercles.
Tuberous root - a generally undistended fibrous root system with thickened fleshy sections scattered along its length. Not a taproot or caudex.
Tubular - in the form of a hollow cylinder.
Turbinate - shaped like an inverted cone or top.
Turgid - swollen by some internal force, usually by fluid uptake.
Turgor pressure - outward force exerted on a cell wall by water taken up into the cell by osmosis.
See also: wall pressure
Type - the permanently preserved specimen or specimens on which the species or sub-species description is based.
Type locality - the place where the type specimen was collected.